1. Field of the Invention
The present invention relates to a substrate transfer robot, a substrate transfer system, and a method for detecting an arrangement state of a substrate.
2. Discussion of the Background
Japanese Unexamined Patent Application Publication No. 2010-219209 discloses a substrate transfer apparatus (substrate transfer robot) that includes a hand. The hand is provided with a transmission optical sensor to detect an arrangement state of a substrate arranged in a substrate storage cassette. The substrate transfer apparatus (substrate transfer robot) recited in Japanese Unexamined Patent Application Publication No. 2010-219209 includes a transferer arm. At a distal end of the transferer arm, the hand is disposed. The hand has an approximate V shape in plan view (in other words, a shape furcated at the distal end). At a distal end of the hand, the transmission optical sensor is disposed. The transmission optical sensor includes a light emitting device and a light receiving device. The light emitting device emits a beam, while the light receiving device receives the beam. In Japanese Unexamined Patent Application Publication No. 2010-219209, the approximately V-shaped hand (light emitting device and light receiving device) is moved to a position below the substrate arranged in the substrate storage cassette and then is moved upward. Here, the substrate transfer apparatus detects an arrangement state of the substrate arranged in the substrate storage cassette (examples of the arrangement state including presence or absence of the substrate, posture of the substrate, and protruding state of the substrate from the cassette) based on whether the light receiving device has received the beam.
In conventional substrate transfer apparatuses (substrate transfer robots) such as the substrate transfer apparatus recited in Japanese Unexamined Patent Application Publication No. 2010-219209, the arrangement state of the substrate arranged in the substrate storage cassette is detected with a hand center line (which is a straight line connecting between the turning center of the hand and a substrate holding center, which is the center of the holding of the substrate by the hand) located in a direction perpendicular to the front surface of the substrate storage cassette in plan view.